The present invention relates to radio frequency (RF) impedance matching, and more particularly, to an RF impedance matching network controller.
The performance of an RF antenna is largely influenced by the amount of its impedance. A mismatch of impedance between the antenna impedance and the impedance of a transmission medium can significantly reduce both transmitted and received power of the antenna. Furthermore, an RF antenna is susceptible to significant change in its impedance in response to electromagnetic material coming within close proximity.
To remedy impedance mismatching in an RF antenna, an impedance matching network is attached between the RF antenna and the transmitter or receiver to match their respective impedance. Additionally, the impedance matching network is able to dynamically match the impedance via a controller as the RF antenna's impedance changes.
FIG. 1 illustrates an RF communication system 100 with conventional tunable impedance matching capability.
As illustrated in FIG. 1, RF communication system 100 includes a transmitter 102, an RF power detection portion 104, a tunable matching network 106, an analog to digital converter (ADC) 107, a microprocessor 108, a digital-to-analog converter (DAC) 109 and an antenna 110. RF power detection portion 104 includes an RF coupler 114 and an RF power detector 116.
Transmitter 102 is arranged to provide an electrical transmission signal 118 to RF power detection portion 104 via electrical connection. RF power detection portion 104 is arranged to provide a transmitted signal 120 based on electrical transmission signal 118 to tunable matching network 106 via electrical connection. Tunable matching network 106 is arranged to provide an output signal 122 based on transmitted signal 120 to antenna 110 and to provide a reflected signal 124 to RF power detection portion 104 via electrical connections. Antenna 110 is arranged to output an electromagnetic signal 126 based on output signal 122.
ADC 107 is arranged to receive an analog control signal 128 from RF power detection portion 104 based on reflected signal 124 via an RF coupler 114 and RF power detector 116. ADC 107 is additionally arranged to provide a digital control signal 129 to microprocessor 108. Microprocessor 108 is additionally arranged to provide a digital tuning signal 130 to DAC 109. DAC is additionally arranged to provide an analog tuning signal 131 to tunable matching network 106. RF power detection portion 104, tunable matching network 106, ADC 107, microprocessor 108 and DAC 109 together provide conventional tunable impedance matching capability to transmitter 102 and antenna 110.
Transmitter 102 may be any known RF transmitters or receivers. RF power detection portion 104 may be any known circuits that detect the power level of an RF signal. RF coupler 114 may be any known coupling device that couples transmission power. RF power detector 116 may be any known devices that measure transmission power.
Tunable matching network 106 may include any known circuits or devices that provide impedance matching between a load and a source. Microprocessor 108 may be any known processors, a non-limiting example includes field-programmable gate array (FPGA). Antenna 110 may be any known antenna with an antenna impedance that varies as a function of ambient electromagnetism.
In operation, transmitter 102 transmits electrical transmission signal 118 with an associated transmission power when there is a radio signal to be transmitted. Transmitter 102 transmits electrical transmission signal 118 to RF coupler 114. RF coupler 114 in turn outputs transmitted signal 120 to tunable matching network 106. As transmitter 102 is connected to RF power detection portion 104 electrically, which in turn also connects to tunable matching network 106 electrically, tunable matching network 106 experiences a source impedance Z1 caused by the electrical connections. Antenna 110 has a variable antenna impedance Z2 that varies as a function of ambient electromagnetism. If there is a mismatch between Z1 and Z2, some of the transmission power from electrical transmission signal 118 will be reflected back toward transmitter 102, thus reducing the performance of antenna 110.
Tunable matching network 106 matches source impedance Z1 and antenna impedance Z2 before transmitting output signal 122 to antenna 110. Tunable matching network 106 matches impedance by adding tunable impedance Z3 with antenna impedance Z2 to compensate for any changes in antenna impedance Z2. As a result, the combination of tunable impedance Z3 and antenna impedance Z2 will match with source impedance Z1, ensuring maximum transfer of power to antenna 110 and to minimize reflected signal 124.
As antenna impedance Z2 changes due to change in ambient electromagnetism, tunable matching network 106 continuously outputs reflected signal 124 based on antenna impedance Z2 and tunable impedance Z3 as reflected power to RF power detection portion 104 to keep matching source impedance Z1 and antenna impedance Z2.
Tunable matching network 106 modifies tunable impedance Z3 via analog tuning signal 131 from microprocessor 108. Microprocessor outputs tuning signal 130 based on digital control signal 129 from RF power detection portion 104.
RF power detection portion 104 generates control analog signal 128 based on transmission power from electrical transmission signal 118 and reflected power from reflected signal 124. RF coupler 114 couples reflected signal 124 to generate a transmission power signal 132. RF coupler 114 then transmits transmission power signal 132 to RF power detector 116 for measurement. Based on the amplitude of transmission power signal 132, RF power detector 116 outputs analog control signal 128 to inform microprocessor 108 if any modification is needed to tunable impedance Z3.
When impedance matching is completed by tunable matching network 106, tunable matching network 106 outputs output signal 122 to antenna 110 for transmission. Finally, antenna 110 outputs electromagnetic signal 126, which is based on electrical transmission signal 118, to its destination.
A problem associated with RF communication system 100 with conventional tunable impedance matching capability in FIG. 1 is the relatively high power usage, high response, and complexity associated with microprocessor 108 in order to control tunable matching network 106.
What is needed is a system to perform impedance matching for use with a transmitter and an antenna that offers low power usage, low response time, and simplicity.